A cam follower of this type is apparent from U.S. Pat. No. 6,382,173 which is considered to form the generic type. Here, a switchable cam follower is likewise proposed which transmits an elevation of a cam to a gas exchange valve of the internal combustion engine via housing parts which can be displaced telescopically into one another and can be coupled to one another, depending on the locking state, or is switched off for the purpose of bringing the gas exchange valve to a standstill. Here, an embodiment which is claimed in accordance with FIG. 1 of this document shows an outer part, in the guide hole of which an inner part is guided longitudinally movably with a run-on surface for the cam. Here, the resilient spacing of the outer part to the inner part is effected by a lost motion spring which is arranged on the outer circumference of the cam follower.
In this embodiment, it is a disadvantage that the ratio of the outer guide length to the outer diameter of the outer part is low, with the result that the inner part with a section facing the cam also has to contribute to the guiding of the cam follower in its housing hole in the internal combustion engine. As a consequence, however, the cam follower would have to have a double fit which is unfavorable in terms of manufacturing technology, as the outer part and the inner part have to be arranged sufficiently coaxially both respect to the housing hole and with respect to the mutual guidance.
Moreover, it is to be considered disadvantageous in this solution that there is a large-volume annular space between the outer part and the inner part, which annular space is open toward the housing hole in the internal combustion engine and during operation also feeds hydraulic medium for actuating the coupling means. A dead volume of this type is, however, unfavorable to the extent that, in the case of the usually present hydraulic medium and, in particular, in the case of a high content of gas bubbles in the hydraulic medium, the rigidity of said hydraulic medium is reduced and thus the dynamics, the reproducibility and the reliability of the switchover operation of the coupling means are impaired.
A further disadvantage results from the position of the coupling means within a cam follower of this type relative to the cam of the internal combustion engine. As the coupling means have a radial installation space requirement which is only insubstantially smaller than the outer diameter of the outer part, they are to be arranged on the other side of the lost motion spring, relative to the cam. As a consequence, the length of a sealing gap is very small between an opening in the outer part for supplying hydraulic medium to the coupling means and an opening of the housing hole which is remote from the cam, with the result that, in particular in the region of the maximum stroke of the cam follower, the risk can occur of an undesirably high pressure loss via leakage of the hydraulic medium into the surroundings of the housing hole. Moreover, there is also the risk of carrying along air or gas bubbles from the surroundings of the housing hole and enclosing them in the annular space which is filled with hydraulic medium, which has the abovementioned disadvantageous effect on the rigidity of the hydraulic medium.